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UNIT A: Energy and Matter Exchange in the Biosphere General Outcome 1: Explain the constant flow of energy through the biosphere and ecosystem. Ecology (Greek – a house or a home): The study of relationships between living things (organisms) and their non-living surroundings (the environment). [1866 Ernst Haeckel] System: an object or group of objects that a scientist chooses to study. Everything other than the system is referred to as the surroundings. Systems are separated from their surroundings by a boundary (distinct or gradual). Open systems: allows both energy and matter to cross the boundary. Closed systems: only allows energy to cross the boundary. Biosphere: all of the areas on Earth that are inhabited by and support life. It is composed of three main areas (Atmosphere, Geosphere (Lithosphere), Hydrosphere). Section 1.1: How energy Enters the Biosphere Energy enters the biosphere from the Sun, through a process of photosynthesis (or from minerals through chemosynthesis). Photosynthesis is the chemical process within plants that converts solar energy into chemical energy. During this process carbon in the atmosphere (CO2) is chemically altered to produce the high energy compound glucose (C6H12O6). Carbon dioxide + water CO2 H2O carbohydrates + oxygen C6H12O6 O2 Energy Input: Sunlight Solar Radiant Energy reaching the Earth: 30% is reflected back (Albedo Effect – reflection of energy from light colored matter; clouds, atmospheric dust, water surface, ice, snow, sand, etc.) 19% is absorbed by gases (water vapour, carbon dioxide, methane, etc.). Some of this absorbed energy heats the atmosphere, while some is radiated back into space. 51% reaches the Earth’s surface and is absorbed by land, oceans, and plants. This heats the Earth’s surface. The resulting heat radiates upward into theatmosphere – where it is either absorbed by atmospheric gases (greenhouse gases) or radiated out to space. Of the energy absorbed by Earth, only a small portion is used for photosynthesis. Of the total radiant energy reaching the Earth, 1-2% is used for photosynthesis. This allows producers to generate ~ 150-200 billion tones of organic matter each year. Energy Output: chemical energy (glucose/starch/carbohydrates) Since plants make their own energy, they are referred to as autotrophs (self feeders) or producers. Most of the chemical energy made by the plant is used by the plant for life functions (movement, growth, repair, transport, reproduction, exchange of materials with the environment, response to stimuli). Some of the chemical energy is stored for future use (usually as starch). Chemosynthetic Producers (chemotrophs) convert inorganic chemicals (minerals, hydrogen sulfide) into organic energy. These organisms are usually found in extreme environments (volcanic deep-sea vents, cold-water seeps, hot springs, intensely salty lakes, deep caves). Chemotrophs (tube worms) living on or around the volcanic deep-sea vents (black smokers which release hydrogen sulfide, minerals, and heat into the water) have no access to sunlight, are heat-resistant, and contain bacteria within their tissues that are able to split the hydrogen sulfide in order to capture the chemical energy. Sulfuric acid is produced as a by-product. Another example of a chemotroph is nitrifying bacteria within soil. They convert ammonia (NH3) in the soil to other nitrogen compounds (nitrate ions and nitrite ions – same as in fertilizer) which are then used by other plants and micro-organisms. When other organisms eat plants, it is the stored energy from the plant that is converted to usable energy for the organism through the process of cellular respiration. Cellular respiration is the process of converting the chemical energy of high energy compounds (glucose) into ATP (adenosine triphosphate). This is a combustion reaction that also releases heat. Carbohydrates + oxygen carbon dioxide + water + heat Energy Input: chemical energy (glucose/starch/carbohydrates) Energy Output: chemical energy (ATP) and heat Organisms that must eat plants (or other organisms) to obtain energy are referred to as heterotrophs (other feeders) or consumers. Consumers are classified based upon how they obtain their food, although many organisms can obtain food from multiple sources: By eating plants and other organisms, the energy from the sun is transferred throughout the biosphere, while matter is constantly recycled through the biosphere. Herbivores – consume primarily plants (primary consumers) Carnivores – consume the flesh of other animals. - Secondary consumers – consume mainly herbivores Tertiary consumers – consume secondary consumers Decomposers – obtain energy-rich molecules from eating/absorbing left-over or waste matter. - Feces Dead organisms/body parts Decomposers return organic and inorganic matter to the biosphere which can then be re-used by producers. Energy Transfer has a one-way flow: First Law of Thermodynamics: energy cannot be created or destroyed. It can only be converted from one form to another, or transferred from one object to another. Second Law of Thermodynamics: With each conversion or transfer of energy, there is less energy available to do useful work because some energy is lost as heat. Eventually, with enough conversions, there will be no useful energy left within the system. Therefore a constant supply of energy is needed to sustain life. Section 1.2: How Energy is Transferred in the Biosphere Ecosystems (Ecological System) – made up of all the organisms that live in an area (biotic factors – organisms, their wastes and remains) and the physical environment of that area (abiotic factors – sunlight, water, minerals). The biotic and abiotic interactions form a self-regulating system through which energy and matter are transferred. 1920’s – Charles Elton and Victor Summerhays studied organisms on an island off the coast of Norway (Bear Island). The island was desolate, and the researchers were able to easily observe the organisms on the island and their feeding interactions. They came up with the concepts of food chains and food webs to describe the feeding interactions they were seeing. As well, they recognized a pattern between the trophic levels of organisms (energy available at each trophic level) and the number (and/or size) of the organisms at each trophic level. Food Chain: a model describing the linear pathway through which food (energy) is transferred from producers to primary consumers to higher trophic levels. These best describe the specific feeding actions of individual organisms. Food Webs: a model of food (energy) transfer in an ecosystem that shows the multiple connections between organisms since organisms (consumers) may prey on more than one species. Food chains and food webs generally have only a few trophic levels (between 3 and 6) because of the limits on the transfer of energy (second law of thermodynamics). When an organism eats other organisms, most of the energy obtained is used for life functions, some is lost as heat, and a small amount is stored. As well, often the consumer doesn’t ingest all of its prey. Generally, the efficiency of energy transfer from one trophic level to another varies between 5-20%. For the purpose of convenience, ecologists assume 10% of the energy is transferred between trophic levels. This is called the Rule of 10. Ecological Pyramids: the pattern between the number/size/mass of trophic levels and the energy available at each trophic level. Pyramid of Numbers: General pattern - animals at higher trophic levels are fewer in number than organisms at lower trophic levels. Limits - when producers are very large (trees), the number of producers may be smaller than the number of primary consumers. Pyramid of Biomass Biomass is the dry mass of living (or once-living) organisms per unit area (g/m2), and indicates the amount of energy present in the living tissue of a trophic level or ecosystem. General pattern –Lower trophic levels have greater biomass than higher trophic levels. Limits – o scientists may define biomass in different ways o Ocean ecosystems – the biomass of the producers (phytoplankton) may be less than the biomass of primary consumers (zooplankton) because the producers are eaten as quickly as they reproduce. Pyramid of Energy Shows the total amount of energy that is transferred through each trophic level, and clearly demonstrates how little energy is left at the highest trophic level. General pattern – lower trophic levels always have more energy than higher trophic levels. Note: the stability of feeding relationships in ecosystems decreases with a decrease in the number or species (biodiversity) – especially the number and variety of producers. Decreases in biodiversity may result from: Loss of habitat Over hunting/fishing Increased stress or competition between species Biomagnification of toxins through the trophic levels of an ecosystem General Outcome 2: Explain the cycling of Matter through the Biosphere Section 2.1: The Role of Water in Cycles of Matter Biogeochemical Cycles: the routes that matter (water and chemical nutrients) take as they are recycled through the biotic and abiotic components of the biosphere. Elements that can easily travel between both water and air can be cycled globally (oxygen, carbon, nitrogen, and sulfur). Nutrient Reservoirs – at each step in a biogeochemical cycle, substances are temporarily stored – in organisms, soil, air, or water. Rapid Cycling – When substances cycle between nutrient reservoirs relatively quickly. Slow Cycling – When substances accumulate and are unavailable to organisms. Hydrologic Cycle – The Water Cycle Water is vitally important in the biosphere due to its chemical and physical properties: Universal solvent due to its hydrogen bonding and polarity Relatively high melting point and boiling points (high specific heat capacity) Water has hydrogen bonding – which causes it to expand when frozen (ice has a lower density than water) Has special adhesive (attraction of water to other substances - dissolving) and cohesive (attraction of water to itself – surface tension) properties Section 2.2: Biogeochemical Cycles The Carbon and Oxygen Cycles Carbon and oxygen are interconnected through the biotic processes of photosynthesis and cellular respiration. Plants consume more carbon dioxide than is released from living organisms. However, carbon dioxide is released into the atmosphere in much greater amounts by the processes of decomposition, forest fires, and human activities. Oxygen is rapidly cycled throughout the biosphere. Carbon can be rapidly cycled, or can be stored in nutrient reservoirs called carbon sinks (trees, sediment, fossil fuels) for hundreds to millions of years. Deforestation = returns 2 gigatones (Gt) of carbon to atmosphere each year Oceans trap 38 000 Gt of carbon in dissolved carbon dioxide Ocean floor sediment = holds 11 000 Gt of carbon as methane hydrates. Since the industrial revolution (late 1800’s) atmospheric carbon dioxide levels have increased by 30% The Sulfur Cycle All organisms require sulfur for the formation of proteins and vitamins. Plants/algae – use sulfate (SO42-(aq)) decomposition releases the sulfur as hydrogen sulfide (H2S) which causes the sulfur smell. Bacteria use sulfur compounds in photosynthesis and cellular respiration o Sulfate reducers convert sulfate to sulfide o Sulfur oxidizers convert sulfide to elemental sulfur and sulfate o Waste that is generated from one type of bacteria becomes the required material for a different type of bacteria. Some sulfur in the soil is stored as sediment (rocks and fossil fuels) which is then released into the atmosphere when high sulfur containing fossil fuels are burned, or through volcanic activity. o Released as sulfur dioxide (SO2) o Sulfur dioxide reacts with water and oxygen in the atmosphere to form sulfurous acid (H2SO3) and sulfuric acid (H2SO4) acid deposition or acid rain. The Nitrogen Cycle Nitrogen gas makes up the majority of our atmosphere (78.1%) and is biologically inert – most living organisms cannot use nitrogen when it is in its elemental form (N2). However, living organisms need nitrogen for the formation of proteins, enzymes, and DNA. Bacteria in the soil (nitrogen fixers) can convert nitrogen gas into ammonium (NH4+) which is then taken up by plants (fertilizer). These bacteria are found in nodules along the roots of legumes. Ammonium is also produced when decomposers break down organic matter – nitrogen in the waste/dead organism is converted from proteins/DNA into ammonia ammonification. Some soil bacteria convert nitrite (NO2-) to nitrate (NO3-). Nitrate is also used by plants to promote growth. Denitrifying bacteria convert nitrite or nitrate back into nitrogen gas. This process of denitrification occurs in low oxygen environments. The Phosphorus Cycle Phosphorus is an essential nutrient, but is available in limited quantities in the environment. It is concentrated in living organisms (DNA, ATP, used heavily in metabolic pathways – phosphorylation, and found in bones and teeth). Phosphorus does not cycle through the atmosphere – it is found only in soil and water. Animals obtain phosphorus by consuming other organisms. Producers can only obtain phosphorus if it is in the form of phosphate (PO43-). The scarcity of phosphorus keeps algae growth in balance. o Human activities increase phosphate in the environment through waste (feed lots), fertilizer use, and detergent use. o This excess phosphate enters the water through runoff or improperly treated waste water and causes massive growth of algae (algal bloom). The bloom of algae blocks sunlight to other aquatic plants these plants die and are decomposed Decomposition of organic material in water causes a decrease in oxygen (the decomposers use up the oxygen) The large mass of algae also starts to die, increasing the organic waste in the water decomposition occurs Oxygen levels drop rapidly Organisms (aquatic invertebrates, vertebrates like fish) do not have enough oxygen and they die fish kills. All the biogeochemical cycles are linked – through water and through the biotic components of the biosphere. They are also linked to the transfer of energy (chemical energy, trophic levels, etc) through the biosphere. An imbalance in one will cause subsequent effects in the others. General Outcome 3: Explain the balance of energy and matter exchange in the biosphere, as an open system, and explain how this maintains equilibrium Section 2.3: The Balance of the Matter and Energy Exchange Net Productivity – the total amount of radiant energy that is transformed to chemical energy by producers minus the amount used by the producers during cellular respiration. Remember – there is a constant input of energy into the biosphere from the Sun and a constant output of radiant energy (heat) to space. Productivity – the rate at which an ecosystem’s producers capture and store energy within organic compounds over a certain length of time. Measured in energy per area per year [J/m2/a] Can be expressed as the biomass of vegetation ADDED to an ecosystem per area per year [g/m2/a] o The rate at which organisms produce new biomass The rate of productivity in terrestrial ecosystems depends upon: o Number of producers present in the ecosystem o The amount of heat o The amount of light o The amount of rainfall – moisture is the key limiting factor in productivity in terrestrial ecosystems. In the ocean, productivity depends upon: o The available nutrients Obtained from estuaries (the mouth of rivers into the oceans) Obtained from upwelling zones on the west side of continents Obtained from the seasonal melting of ice The available sunlight – the amount of solar radiation - limits a regions productivity Homeostasis – the state of equilibrium, or balance. Individual organisms must maintain steady conditions (within certain limits or range of tolerance) in order to live. Ecosystems also must be in balance for organisms to thrive. (Predators and prey, biogeochemical cycles, climate change) Gaia Hypothesis (James Lovelock, 1979) – considers homeostasis on a global level. o Proposed that the biosphere acts like an organism – in that it is self regulating within its range of tolerance (it maintains environmental conditions within certain limits). o Both the biotic and abiotic components of the biosphere are involved in maintaining or changing the conditions. Living thing affect non-living conditions, and non-living conditions affect living things. Ex. The presence of humans in a room causes and increase in carbon dioxide the increased carbon dioxide causes people to yawn more and feel sleepy. Evidence of how life has affected the biosphere: Stromatolites – sedimentary rocks formed from ancient mats/beds of micro-organisms. (3.8 – 2.5 billion years ago) o The atmosphere lacked free oxygen (oxygen only present in mineral compounds) -Anoxic o Non-oxygen using bacteria and micro-organisms grew – forming mats / beds o The bacteria utilized ions dissolved in the shallow oceans – iron ions were present in larger amounts. Iron ions react with oxygen readily, so any oxygen in the water was trapped by the iron, and then taken in by the bacteria. o Around 2.5 billion years ago, the iron sediments increased, suggesting more oxygen available to react with iron – due to the activity of photosynthetic organisms like cyanobacteria o After 1.8 billion years ago the iron oxides disappear, suggesting no more iron ions in the water – with the oceans iron store depleted, the oxygen produced by the bacteria was free to build up The difficulty of replicating the complexity of Earth’s Biosphere: Biosphere 2 – a large scale experiment where researchers tried to create an artificial, selfregulating and homeostatic biosphere. o Partly to better understand the interactions of our own biosphere o Partly to prepare for sustainable space travel and planet colonization. o Designed for researchers to live in the biosphere completely self-contained for 2 years. Included: o Plants/producers – from algae and phytoplankton to crops To produce oxygen and remove carbon dioxide, and to filter water o Consumers – humans, micro-organisms (decomposers), and entire food chains Result: o Researchers were only able to live in the biosphere for a few months before oxygen levels dropped and carbon dioxide levels became dangerous. o Showed that energy and matter exchange in our biosphere is a very complex, delicate, and interrelated system. o Similar projects have moved forward from the Biosphere 2’s information. ALS (NASA’s Advanced Life Support) program to research how plants may be grown in a space colony for food and oxygen regeneration. International field project on Devon Island in the Canadian Arctic that models a hypothetical colony on Mars – includes living and research facilities as well as a fully enclosed greenhouse. Human Activities on the Biosphere The “control of Nature” is a phrase conceived in arrogance, born of the Neanderthal age of biology and philosophy, when it was supposed that nature exists for the convenience of man. - Rachel Carson, Silent Spring Dead Zones – regions of lakes or oceans in which aquatic life has suffocated due to algal blooms. Approximately 150 dead zones in the oceans May occur seasonally Pollution also contributes to algal blooms o Erosion of soil nutrients o Sewage o Surface run-off o Chemical fertilizer use o o o o Persistent chemicals – especially persistent organic pollutants (POP’s) like PCB and DDT can continuously cycle through the environment and become biomagnified in food chains. Solutions to removing pollutants/excess nutrients from water Wetlands – act as filters. Plants utilize or uptake a large proportion of the nutrients and pollutants before the water moves into oceans or lakes. o Bogs, marshes, swamps o Many wetlands destroyed to allow for human homes/roads, etc Calcutta, India o One of the most populated cities in the world – vast amounts of sewage o Built a vast network of canals and wetlands to treat the city’s sewage o Algae and bacteria in the wetlands feed on the organic material o Fish have been added to feed on the algae to prevent algal blooms o People can support themselves by growing vegetables or fishing in the wetlands, then selling the produce and fish Phytoremediation Using the natural ability of plants and micro-organisms to degrade or remove contaminants from soil and water. This can be a somewhat slower process, as plants can only grow at a specific rate. However, using fast-growing plants like bamboo or weeds can speed up the process, or using micro-organisms which rapidly reproduce. The contaminants become incorporated into the organism’s tissues – often converted to nonharmful compounds, but not always.